1. Field of the Invention
The present invention relates to a stereoscopic television system that can prevent the optical axes of a plurality of camera units disposed in the television system from deviating from their correct paths and thus provide stereoscopic images of an object.
2. Description of the Prior Art
Some work sites, such as the deep sea and space, are hardly accessible by worker, or some work sites such as nuclear reactors may risk the safety of workers. To work in a hazardous environment or at such inaccessible sites, a manipulator is useful. The manipulator is remotely controlled by operators who are positioned at a safe distance far from the work site.
According to this technique, the image of the work site (work environment) is taken by camera units, and images of the work site are stereoscopically displayed on a display units such as a monitor television unit. Viewing the images on the display unit, the operator remotely controls the manipulator.
FIG. 1 is a view showing a conventional stereoscopic television system for providing stereoscopic images of a work site for the purpose of remote control.
The stereoscopic television system of FIG. 1 comprises a right camera unit 101a, a left camera unit 101b, an image mixer 102, a frame converter 103, a shutter-spectacles driver 104, shutter-spectacles 105, and a monitor television unit 106. The two camera units 101a and 101b are horizontally arranged side by side on a universal head (not shown) to simultaneously photograph a front object 107. The camera units 101a and 101b are provided with optical systems 101c and 101d, respectively. Each optical system generally comprises a zoom lens.
Light from the object 107 passes through the optical systems 101c and 101d to form images on image pickup elements (not shown) of the camera units 101a and 101b. Then, the image pickup elements send video signals to the image mixer 102, from which the video signals are alternately outputted at predetermined intervals to the frame converter 103. The frame converter 103 carries out a flickerless process on the video signals to remove flicker from the images. Then, the video signals are alternately provided for the monitor television unit 106.
A viewer 108 senses stereoscopic images from the images displayed on the monitor television unit 106 through the shutter spectacles 105 whose left and right spectacles are alternately opened and closed according to synchronous signals provided by the frame converter 103. Namely, the stereoscopic television system of this arrangement utilizes the afterimages in human eyes to provide the sense of stereoscopic images.
When the viewer 108 wants to have an image of wide-view angle or tele-view-angle through the zoom lenses of the optical systems 101c and 101d, the viewer 108 may operate a lens controller 109. If the operator wants to adjust a distance between the camera units 101a and 101b or a viewing angle of the object 107, the viewer 108 may operate a universal head controller 110.
To let the viewer 108 sense stereoscopic images from the stereoscopic television system of such an arrangement, it is necessary to align the images projected on the left and right eyes of the viewer 108 with each other in the magnifications, positions, postures, etc., of the images. To do so, optical axes of the optical systems 101c and 101d extending to the image pickup elements (not shown) are set in a plane that includes the camera units 101a and 101b.
When the optical systems 101c and 101d comprise zoom lenses, the optical axes of the zoom lenses are stationary even if their zooming magnifications are changed. To realize this, the lenses shall be carefully selected and precisely positioned. In practice however, it is very difficult to prepare lenses of equal properties and to strictly maintain their setting positions under external influences.
Namely, if the conventional stereoscopic television system employs zoom lenses for its optical systems 101c and 101d, the optical axes of the lenses tend to deviate from their correct paths. Particularly when the zoom lenses are operated to zooming positions, the optical axes may greatly deviate from their correct paths. Then, images projected on the left and right eyes of the viewer 108 will not align with each other, and the viewer cannot correctly sense stereoscopic images.
When the stereoscopic television system is used in hazardous environment to remotely control a manipulator and if the system causes such deviations on its optical axes, the observer cannot conceive good stereoscopic images of an object to be handled by the manipulator. This will deteriorate the safety of the work and the operability of the manipulator.
As described above, a the conventional stereoscopic television system comprises a plurality of the camera units 101a and 101b provided with the optical systems 101c and 101d. To align optical axes of the optical systems with their proper paths, the optical systems shall use lenses of equal properties, precisely assembled in the optical systems 101c and 101d. When the lenses are zoom lenses, optical axes of the optical systems 101c and 101d tend to deviate from the proper paths in taking zooming positions. Then, proper stereoscopic images are not adequately provided.